Planographic scraper bar printing press

ABSTRACT

A planographic scraper bar printing press suitable for fine art prints including a motor for driving the printing bed, such motor being positively connected to such bed with a ball screw and ball nut arrangement; a pyramid set of hollow bed support rollers; a motorized scraper bar adjustment; a pressure sensitive switch to shut off such bar motor at a predetermined scraper bar pressure; and switching means to automatically shut off the bed drive motor when the scraper bar reaches the end of the printed paper.

United States Patent 1,860,693 5/1932 Sheedy et a1 l0l/282X 1,669,9725/1928 Cottrell 101/250 X 2,876,001 3/1959 Stenstrom 101/282 X 3,067,67612/1962 Dickerson 101/250 FOREIGN PATENTS 464,719 1/1914 France 101/130358,404 9/1922 Germany... 101/250 553,655 12/1956 Italy 101/250 PrimaryExaminer-Clyde I. Coughenour Attorney-McCoy, Greene & Howell ABSTRACT: Aplanographic scraper bar printing press suita ble for fine art printsincluding a motor for driving the printing bed, such motor beingpositively connected to such bed with a ball screw and ball nutarrangement; a pyramid set of hollow bed support rollers; a motorizedscraper bar adjustment; a pressure sensitive switch to shut off such barmotor at a predetermined scraper bar pressure; and switching means toautomatically shut off the bed drive motor when the scraper bar reachesthe end of the printed paper.

PATENTEUNUV 1971 I 3618.515

' sum 1 OF 2 INVENTOR. THOMAS A SCHOF/ELD BY AR THUR f SCHOF/ELD ATTORNE Y5 PLANOGRAPIIIC SCRAPER BAR PRINTING PRESS BACKGROUND ANDSUMMARY OF INVENTION This invention relates to improvements in printingpresses and more particularly to an improved low-cost planographicscraper bar lithography printing press for producing so called fine artprints.

Fine art printing is a highly specialized field characterized in thatthe artist himself designs the print and publishes it in limitededitions under his supervision. The finished prints bear the artistssignature and normally command a high price.

Fine art prints are sought after by art collectors and numerous suchprints hang in known art collections around the world. Not to beconfused with common mass-printed reproductions," fine art prints arepainstakenly prepared and must be of the highest quality and uniformity.

The prints are prepared by the artist who draws the image to be printeddirectly on a printing plate or a Bavarian Litho Stone. The plate orstone is then treated to make the image ink receptive. Ink is applied tothe plate or stone with the closest attention directed to full coverageand even application. Once the plate or stone is inked, the paper to beprinted is carefully set upon it and covered with a thick blotter andoverlaid with a thin rigid board which is greased along its uppersurface. The press scraper bar is also greased and then applied againstthe greased board at between about 1,800 and 2,400 p.s.i. The bed isthen actuated to draw the bed beneath the bar causing the image to betransferred to the paper. The paper is then removed, the plate isreinked, a fresh sheet of paper inserted, and the process repeated untilthe desired number of copies have been made or until the printing platewears out.

Since only one color can normally be printed on the paper at one time, amulticolor print normally requires a separate drawing on plate or stonefor each color employed, and separate printing runs are made with eachplate or stone.

In order for the prints to meet art quality standards, it is absolutelyessential that the printing press employed be of the highest quality andproduce uniform prints without blurring or distortion. On the otherhand, printmakers do not require fast, high volume production pressesemployed by commercial printers, since fine art printmakers normallyproduce only small quantities of prints per plate, perhaps between 25and 150.

Commercial presses are designed for high volume production and are toocostly for the relatively low volume in which fine art prints areproduced. Inexpensive low volume presses have been devised for use inschools and other institutions and they have been satisfactory forgeneral purposes; however, such presses have not always provided thequality prints sought by skilled printmakers for fine art purposes.

Accordingly, it is the principal object of the present invention toprovide a low-cost lithographic press suitable for producing fine artprints of the highest quality.

A further object of the present invention is to provide lithographicfine art printing press having an antideflection bed support rollersystem to prevent the bed (that portion of the press which carries theplate) from deflecting under pressure of the scraper bar and therebyassure uniform pressure across the plate surface.

Another object of the present invention is to provide an inexpensivelithographic fine art printing press having a bed which is power drivenand positively connected to the power drive, thereby assuring uniformbed speed.

Still another object of the present invention is to provide aninexpensive lithographic printing press which produces line art qualityprints, but which is still simple to operate, lightweight andsufficiently inexpensive that it may also be suitable for schools andother institutions.

Yet another object of the present invention is to provide a press whichis power driven to reduce the amount of manual labor involved inproducing fine art prints and also which can be provided with anautomatic power cutoff to prevent the operator from accidentally runningthe scraper bar past the paper onto the plate or stone.

With the above and other objects in view, the invention consists of theimproved printing press as set forth in the following specification andclaims, and all equivalents thereof.

BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings,illustrating the preferred form of the invention, and wherein likereference numerals designate the same parts in all views:

FIG. 1 is a perspective view of the printing press of the presentinvention showing a printing plate supported on a lifting block on thepress bed.

FIG. 2 is a side elevation, with parts broken away, of the press'shownin FIG. 1, without the lifting block or printing plate.

FIG. 3 is an end sectional elevation of the press shown in FIG. 1,without the lifting block or printing plate.

FIG. 4 is a detail view of one of the ball bushings mounted on theunderside of the press bed and its connection to one of thesupport-guide rods.

FIG. 5 is a detail view of the ball nut mounted on the underside of thepress bed and its connection to the central lead screw, together with asectional view of the bed support rollers.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring in greater detail to thedrawings, the major structural parts of the planographic scraper barpress of the present invention include an upright central frame 1 ascraper bar 2, a movable bed 3, a pyramid set of central bed supportrollers 4, a bed support frame 5, a motor 6 for driving the bed and amotor 7 for raising and lowering the scraper bar.

In operation of the press, a printing plate 8 having the desiredprinting or design thereon lies on a lifting block 33 on the press bed3, and is treated, inked and the paper to be printed is set upon it.Blotter paper (not shown) is laid over the plate, and a thin rigid board(also not shown) placed on top of the blotter paper. The upper surfaceof the board and the lower surface of the scraper bar (which is coveredwith a leather pad) are greased to assist slippage. The bar motor 7 isthen actuated to lower the scraper bar 2 to a point where it willpressurably engage the thin board above the paper on the plate 8. Thebed motor 6 is then actuated to drive the press bed 3 beneath thescraper bar 2, causing the design on the plate 8 to be printed on thepaper. When the scraper bar reaches the end of the paper, the bed motor6 is stopped and the motor 7 is actuated to raise the scraper bar aboutone-half inch from the printing surface. The bed motor 6 is thenreversed to return the bed 3 to its original position where the printedpaper is removed, the plate 8 reinked, a fresh piece of paper inserted,and the operation is repeated.

Where quality art prints are being produced, the number of prints whichcan be made before the plate becomes worn is often relatively small,perhaps on the order of -200 prints.

The upright central frame I includes a pair of parallelspaced verticalside members 9 mounted on either side of the bed support frame 5. Eachpair of side members 9 is capped by a short horizontal bar 10 whichsupport a pair of parallelspaced horizontal top rails 11, L-shaped incross section, which transversely span the bed support frame 5. A steelhousing 12 is centrally mounted between the spaced top rails 11 andprovided with a central vertical aperture.

The scraper bar 2 is removably mounted in a holder 13 having anelongated opening in its bottom surface. A mounting bracket 14 is boltedin the center of the holder 13. The lower end of a vertical lead screwor ball screw 15 is fixedly rotatably secured to the top of the mountingbracket 14 and the lead screw 15 projects upwardly into the centralvertical aperture in the steel housing 12 of the upright central frame1.

The ends of the scraper bar 2 track slidably between the pairs of spacedvertical side members 9 of the upright central frame 1. This braces thescraper bar 2 during the printing operation, and substantially preventsit from deflecting in the longitudinal and angular directions.

The scraper bar 2 is of conventional design, being formed of wood andhaving a beveled lower edge. In operation, a section of leather isstretched across its lower edge. The scraper bar 2 may also beconstructed of plastic, in which case leather is not required. Thescraper bar 2 is removably held in the holder 13 with a central thumbscrew 16, its beveled edge projecting downwardly out of the holderaperture.

The steel housing 12 through which the vertical ball screw 15 passes inthe upright central frame 1 rotatably houses a ball nut (not shown)through which the ball screw 15 is threaded.

The exterior of the ball nut is provided with a spur gear configurationwhich meshes and is driven by the drive gear of a gearbox preferablycoupled to a standard reversible, one-half hp., constant speed, 200 rpm,1 volt, AC motor. Accordingly, when the motor is actuated, the ball nutis driven in rotation about the lead screw and, depending upon thedirection in which it is driven, vertically raises or lowers the scraperbar 2. The vertical lead screw 15 preferably has a onequarter inch pitchand the dimensions and arrangement of the gears cause In the productionof art quality prints, uniform prints are essential. Furthermore, it isoften important to minimize the number of rejected prints inasmuch asthe useful life of the printing plate is limited.

In standard planographic printing operations, both with our press andwith presses of previous design, it is necessary to relieve scraper barpressure each time a print is removed from the plate or stone. Thescraper bar should be reset at roughly the same pressure for each printis uniform prints are to be obtained and to minimize the number ofdefective prints.

In the past, various devices have been employed to provide relativelyuniform scraper bar pressure throughout the printing operation. In somecases, the bed is dropped and raised between two preset positions. Inother cases, the scraper bar is provided with a two-position clutchmechanism which operates independently from the vertical screwadjustment.

We have found we can help to assure high quality uniform prints andminimize defective prints by employing a pressure sensitive switch (notshown) on the motor 7 for raising and lowering the scraper bar. Theswitch we employ is actuated when the electric current drawn by thescraper bar motor 7 reaches a predetermined level. Inasmuch as the motor7 draws current in direct proportion to the pressure it exerts, this isa simple, convenient and inexpensive way to achieve uniform scraper barpressure during printing operations.

The printing bed 3 of my press is steel, preferably of about one-quarterinch thickness, and its upper surface is laminated with a thin (e.g.about 0.040 inch) coating of lucite which provides a stable seat for theprinting plate.

The printing bed 3 is mounted for reciprocating movement in thelongitudinal horizontal plane on a pair of stationary cylindricalsupport-guide rods 18 mounted at the sides of the bed frame 5. Four ballbushings 19 are fixedly mounted on the bottom of the printing bed 3 andthese serve to movably mount the bed 3 on the rods 18.

The drive mechanism for the printing bed includes an elongated leadscrew or ball screw 20 journaled for rotation in the center of the bedframe 5. This lead screw 20 is positioned centrally between and parallelto the stationary guide-support rods at the sides of the frame. Thisrotatable lead screw 20 is provided with a sprocket wheel 21 at one end,and a drive chain 22 operably connects this sprocket 21 to a secondsprocket wheel 23 on the drive shaft of the bed drive motor 6 mounted onthe frame below. The bed 3 is provided with a stationary ball nut 24fixedly mounted in the center of its bottom surface. This ball nut 24receives the lead screw 20, so that when the bed drive motor 6 isactuated to rotate the lead screw, the bed 3 is driven along the lengthof the screw 20, toward one end or the other depending on the directionin which the motor 6 is driven.

The bed drive motor 6 is preferably a standard one-half hp., 1 10 volt,AC, 200 rpm. constant speed reversing motor, and the sprocket ratiois'about l2:l so that the lead screw turns at about 2,400 rpm. The leadscrew has a one-quarter inch pitch, so that the bed 3 is preferablydriven at the rate of about 50 feet per minute. Bed speed may, however,be increased or decreased in accordance with the requisites of theparticular printing operation to be performed, and different drivesystems may be employed within the spirit of the present invention, aswill be apparent to persons ofordinary skill.

It is important, however, that the drive system we employ provides apositive driving connection between the motor 6 and the bed 2, so thatthe bed 2 is driven past the scraper bar 2 at a uniform and constantspeed. In the past, it has been common to employ a manual bed drive or,where motors have been employed, to provide friction drive means whichhave a natural tendency to slip. Both systems result in irregularitiesin bed speed. We have found that such irregularities in the speed of thebed detract from the quality of the prints and/or result in a higherproportion of unacceptable prints, and we have been able to overcomethese problems by providing positive driving connection between the bedand the bed drive motor.

A pyramided set 4 of four central bed support rollers 27 and 28 aremounted beneath the bed 3 in the center of the bed frame 5. Theserollers 27 and 28 consist of a pair of full length parallel adjacentelongated cylindrical lower rollers 27 journaled for rotation in a pairof side plates 29 mounted at the sides of the bed frame 5, and a pair ofhalf-length cylindrical upper rollers 28 freely carried for rotation onthe lower rollers 27. The axes of the upper rollers 28 lie directlybeneath the scraper bar 2, and each roller 28 supports one-half of thebed to reinforce it against deflection at that point under scraper barpressure. The position of the upper rollers 28 is maintained with outerguides which are annular rims 30 on the outer ends of the lower rollers27, and inner guides which are a pair of spaced-parallel elongated ribs31 depending from the lower surface of the bed 3 and extending the fulllength of the bed 3 on either side of the bed drive lead screw 20.

It has been common, in the past, to provide a single bed support rollerin lieu of the pyramid set 4 of rollers we employ. The ends of suchroller have been normally journaled for rotation at the sides of theframe. We have found that the single journaled roller has had a tendencyto deflect or bow slightly under scraper bar pressure. This results inuneven pressure along the length of the scraper bar and is a source ofimperfections in the prints. We have overcome this difficulty with thepyramid multiple roller system described.

It will be apparent that the upper two half length rollers 28 in mypyramid set 4 could be replaced with a single full length roller ifanother equivalent bed drive mechanism were employed. For example, thepair of guide-support rods 18 at the sides could be replaced by a pairof bed drive lead screws driven in tandem from the same motor. Thiswould obviate the need for the central bed drive screw 20, and wouldpermit a single elongated upper roller to be employed. The preciseconstruction of this and other variations in the roller structure,within the spirit of the present invention, will be apparent to personsof ordinary skill.

The rollers 27 and 28 we employ are approximately 4 inches in diameterand formed from hollow steel tubing of about fiveeighths inch wallthickness. The two lower rollers 27 are fitted with end plugs bearingstub shafts for journal mounting in the frame.

Our pyramid multiple roller system is an important factor in keeping theweight and cost of our press within reasonable limits inasmuch as itprovides superior back up support for the bed. Comparable results with asingle roller would require a roller many times heavier and larger thanthe weight and bulk of the multiple rollers we employ, together with aheavier frame and more powerful bed drive system. While the particulardiameter and wall thickness of the rollers shown do not necessarilyproduce optimum antideflection characteristics for the weight of rollersemployed, they are believed to produce near optimum results and areclearly superior to the single roller system of prior art devices. Ifeven less bed deflection is desired, it may be achieved by expanding theroller pyramid to include an additional layer of three rollers journaledin the frame to back up the present two lower rollers, thus expandingthe roller pyramid to a total of seven rollers, the precise constructionof which will be readily apparent to persons of ordinary skill.

Our printing press, being thoroughly motorized, may be provided withadditional electric control devices, the precise construction of whichwill also be apparent to persons of ordinary skill. Such electriccontrols may include a limit switch to stop the bed motor automaticallyat the end of the bed after printing one sheet. Such limit switch couldalso serve to simultaneously actuate the scraper bar motor toautomatically raise the scraper bar once the bed has stopped. Anadditional limit switch may be employed to automatically stop thescraper bar motor once the bar has been raised a sufficient distance,and such limit switch may also serve to simultaneously actuate the bedmotor to automatically return the bed to its start position after thebar has been raised. A third limit switch may be employed toautomatically stop the bed once it reaches the start position. Suchswitching systems may be employed separately or in combination. Itshould be pointed out, however, that the use of a limit switch to stopthe bed at the end of the print is not only a convenience, but guardsagainst damage to the printing plate which may occur if the scraper barpasses the end of the sheet into direct contact with the plate itself.

From the foregoing, it is seen that the present invention provides alow-cost lithographic press which is suitable for fine art prints andotherwise accomplishes its intended objects. It is understood that thepresent invention may be embodied in several forms without departingfrom its spirit or essential characteristics, and that the embodimentsshown and described are illustrative and not restrictive, since thescope of the invention is defined by the appended claims rather than bythe description preceding them, and all changes that fall within thelimits of the claims or their functional equivalents are intended to becovered by these claims.

We claim:

1. A lithographic printing press comprising a main frame having uprightside members and a horizontal transverse top member supported by andbetween said side members;

a transverse scraper bar vertically adjustably suspended from saidhorizontal top member between said side members;

a reversible first motor mounted on said frame;

means operatively connecting said first motor to said scraper bar todrive said scraper bar for said vertical adjustment;

at least three support rollers arranged pyramid fashion including a pairof adjacent horizontally aligned lower rollers journaled for rotation insaid frame, and an upper roller carried by and rotatably supported alongits length by said lower rollers, said upper roller positioned directlybeneath and spaced from said scraper bar;

a flatbed horizontally movably mounted below said scraper bar andsupported on said upper roller;

a reversible second motor mounted on said frame;

means operatively connecting said second motor to said bed, such secondnamed means providing a positive driving connection between said bed andsaid motor.

2. A printing press as recited in claim 1 wherein the second named meanscomprises a ball nut fixedly mounted on the bottom surface of said bed,a second elongated ball screw rotatably secured to said main frame andthreaded through said fixed ball nut, and means positively coupling saidsecond motor to said second ball screw, so that when said motor isactuated, said second ball screw is driven in said fixed ball nut at aconstant angular speed to drive said bed in the longitudinal directionbeneath said scraper bar at a uniform speed.

3. A printing press as recited in claim 1 wherein the first namedoperative connecting means comprises a ball nut rotatably supported onsaid horizontal top member of said frame, an elongated ball screwrotatably secured to said scraper bar and threaded through saidrotatable ball nut, and means coupling said motor to said ball nut, sothat when said motor is actuated, said ball nut is driven in rotationabout said ball screw, thereby raising or lowering said ball screw andsaid associated scraper bar.

4. A printing press as recited in claim 1 wherein said first motor isprovided with a load limit switch so that power supplied to said firstmotor will be switched off when the electric current load drawn by saidfirst motor reaches a predetermined level.

5. A printing press as recited in claim 2 wherein the first namedoperative connecting means comprises a ball nut rotatably supported onsaid horizontal top member of said frame, an elongated ball screwrotatably secured to said scraper bar and threaded through saidrotatable ball nut, and means coupling said motor to said ball nut, sothat when said motor is actuated said ball nut is driven in rotationabout said ball screw, thereby raising or lowering said ball screw andsaid associated scraper bar.

6. A printing press as recited in claim 5 wherein said first motor isprovided with a load limit switch so that power supplied to said firstmotor will be switched off when the electric current load drawn by saidfirst motor reaches a predetermined level.

7. A printing press as recited in claim 1 wherein said support rollersare hollow.

8. A printing press as recited in claim 7 wherein said support rollersare approximately 4 inches in diameter and have a wall thickness on theorder of five-eighths inch.

9. A printing press as recited in claim 5 wherein said support rollersare hollow.

10. A printing press as recited in claim 9 wherein said support rollersare approximately 4 inches in diameter and have a wall thickness on theorder of five-eighths inch.

11. A printing press as recited in claim 6 wherein said support rollersare hollow.

12. A printing press as recited in claim 12 wherein said support rollersare approximately 4 inches in diameter and have a wall thickness on theorder of five-eighths inch.

13. A printing press as recited in claim 1 wherein switching means areprovided to automatically stop said bed drive motor once said bed hasreached a predetermined position upon having been driven beneath saidscraper bar during printing.

14. A printing press as recited in claim 5 wherein switching means areprovided to automatically stop said bed drive motor once said bed hasreach a predetermined position upon having been driven beneath saidscraper bar during printing.

15. A printing press as recited in claim 12 wherein switching means areprovided to automatically stop said bed drive motor once said bed hasreached a predetermined position upon having been driven beneath saidscraper bar during printing.

I It i i i

1. A lithographic printing press comprising a main frame having uprightside members and a horizontal transverse top member supported by andbetween said side members; a transverse scraper bar verticallyadjustably suspended from said horizontal top member between said sidemembers; a reversible first motor mounted on said frame; meansoperatively connecting said first motor to said scraper bar to drivesaid scraper bar for said vertical adjustment; at least three supportrollers arranged pyramid fashion including a pair of adjacenthorizontally aligned lower rollers journalled for rotation in saidframe, and an upper roller carried by and rotatably supported along itslength by said lower rollers, said upper roller positioned directlybeneath and spaced from said scraper bar; a flat bed horizontallymovably mounted below said scraper bar and supported on said upperroller; a reversible second motor mounted on said frame; meansoperatively connecting said second motor to said bed, such second namedmeans providing a positive driving connection between said bed and saidmotor.
 2. A printing press as recited in claim 1 wherein the secondnamed means comprises a ball nut fixedly mounted on the bottom surfaceof said bed, a second elongated ball screw rotatably secured to saidmain frame and threaded through said fixed ball nut, and meanspositively coupling said second motor to said second ball screw, so thatwhen said motor is actuated, said second ball screw is driven in saidfixed ball nut at a constant angular speed to drive said bed in thelongitudinal direction beneath said scraper bar at a uniform speed.
 3. Aprinting press as recited in claim 1 wherein the first named operativeconnecting means comprises a ball nut rotatably supported on saidhorizontal top member of said frame, an elongated ball screw rotatablysecured to said scraper bar and threaded through said rotatable ballnut, and means coupling said motor to said ball nut, so that when saidmotor is actuated, said ball nut is driven in rotation about said ballscrew, thereby raising or lowering said ball screw and said associatedscraper bar.
 4. A printing press as recited in claim 1 wherein saidfirst motor is provided with a load limit switch so that power suppliedto said first motor will be switched off when the electric current loaddrawn by said first motor reaches a predetermined level.
 5. A printingpress as recited in claim 2 wherein the first named operative connectingmeans comprises a ball nut rotatably supported on said horizontal topmember of said frame, an elongated ball screw rotatably secured to saidscraper bar and threaded through said rotatable ball nut, and meanscoupling said motor to said ball nut, so that when said motor isactuated said ball nut is driven in rotation about said ball screw,thereby raising or lowering said ball screw and said associated scraperbar.
 6. A printing press as recited in claim 5 wherein said first motoris provided with a load limit switch so that power supplied to saidfirst motor will be switched off when the electric current load drawn bysaid first motor reaches a predetermined level.
 7. A printing press asrecited in claim 1 wherein said support rollers are hollow.
 8. Aprinting press as recited in claim 7 wherein said support rollers areapproximately 4 inches in diameter and have a wall thickness on theorder of five-eighths inch.
 9. A printing press as recited in claim 5wherein said support rollers are hollow.
 10. A printing press as recitedin claim 9 wherein said support rollers are approximately 4 inches indiameter and have a wall thickness on the order of five-eighths inch.11. A printing press as recited in claim 6 wherein said support rollersare hollow.
 12. A printing press as recited in claim 12 wherein saidsupport rollers are approximately 4 inches in diameter and have a wallthickness on the order of five-eighths inch.
 13. A printing press asrecited in claim 1 wherein switching means are provided to automaticallystop said bed drive motor once said bed has reached a predeterminedposition upon having been driven beneath said scraper bar duringprinting.
 14. A printing press as recited in claim 5 wherein switchingmeans are provided to automatically stop said bed drive motor once saidbed has reach a predetermined position upon having been driven beneathsaid scraper bar during printing.
 15. A printing press as recited inclaim 12 wherein switching means are provided to automatically stop saidbed drive motor once said bed has reached a predetermined position uponhaving been driven beneath said scraper bar during printing.